Understanding your laser power detector spec sheets
Tuesday, May 08, 2018
Our blog post this week is intended to give you an oversight of the different elements covered by our specifications sheet. As you may have already heard before, knowledge is power: better understanding your current or future Gentec-EO products is key to knowing what you’re getting and doing.
In this first iteration, we will cover power detectors in particular. They appear in yellow in the catalogue and and are generally considered to be our bread and butter. They are diverse, efficient and easy to use, but it still really pays off to be fully aware of their specifications and what they mean to you.
Our UP19-H series is one of the more popular product lines we offer. We will therefore use it as our reference for this article.
In the catalogue, the left page of a line of products provides the main features of the products, along with useful information to find compatible accessories and related products. The right page is where you’ll find the detailed specifications.
First off, the top section displays all models available within a family of products. The way we divided our product series makes it so that the maximum measurable average power is generally the single element that varies from left to right (maximum power is increasing towards the right). There are however exceptions.
Maximum average power always appears as two values separated by a slash. The first value represents the maximum average power the device can withstand continuously, while the second is for 1 minute. The device will handle such a power level continuously if it is used within specifications.
Therefore, an environment with extreme temperatures would cause this value to shift, and it may induce a bias in your measurements if these conditions are extended. Note that we can help you determine the maximum average power a device can take over a period of time different than 1 minute; contact your Gentec-EO representative to learn more.
Effective aperture should speak for itself, but you should be aware that we do not recommend to cover more than 80% of the total area with your laser beam.
Cooling method refers to the cooling module that is generally placed at the back of the detector to allow its proper cooling in consequence of the input laser power. When it comes to power meters in the yellow section in our catalogue, water is never used as the medium in which heat is measured.
In other words, calorimetry is not the method being used here: the water exclusively acts as a cooling mechanism. Still, there are water specifications that need to be followed, and this is covered in the UP series manual.
The next section is about the measurement capabilities of the device. This section generally causes questions to be raised, which are legitimate because of the technical nature of the specifications shown.
Spectral range refers to the laser wavelength values at which the device will function. Technically, it works in a much broader range than what is shown here, so we have instead defined the spectral range as the range of wavelengths to which a detector is reasonably sensitive and reasonably flat in terms of absorption.
The calibrated spectral range refers to the range in which the device is traceable to a standard (NIST) and for which we can specify an uncertainty. This is covered instead in our user manuals.
Noise equivalent power (NEP) is an intrinsic, parasitic signal that is randomly generated by the device. It is generally very low compared to the maximum average power the device can measure, but should it still be required to measure low powers with a bigger power head, one can find the minimum measurable power by defining an acceptable signal-to-noise ratio (SNR) to the NEP.
Industry standards generally consider a SNR of 30 to be safe, with 20 being common as well. Anything below 20 is widely accepted as intolerable. In other words, the noisy nature of the device would have too much influence on the accuracy in such a case.
Rise time refers to the time it takes for the analog voltage output of the power head to reach 95% of the input laser power value (considering that voltage is equivalently powered for such a device).
Fast rise times (the value being shown) are possible thanks to our anticipation algorithm, which manages to estimate with high confidence the expected value, in spite of the slower thermal sensing technology being used. This is achieved by pairing the detector with a meter.
Sensitivity is the number of volts generated by the input laser wattage. This is generally useful only for advanced users intending to use the raw voltage output of the power head.
For all practical purposes, the calibration uncertainty corresponds to the measurement uncertainty of your device. For example, if your calibration uncertainty is more or less 2.5% and your measurement is 100W the real power value of the laser may be contained between 97.5W and 102.5W.
The energy mode on power meters refers to its capacity to measure very high amounts of energy (Joules) in single shot mode only. You should contact a Gentec-EO representative if you have such an application and are unsure about the elements being covered here. As it stands, we will cover this topic better in our eventual iteration of the same text for energy detectors.
The following section is about damage thresholds. As you can imagine, even our power detectors can fail under very heavy conditions.
Maximum average power density and maximum energy density (pulsed laser damage thresholds) add the conception of beam size to the mix. It is a very common practice in our industry to ensure the beam size is sufficiently large during measurement: this primordially helps stay below the damage thresholds, but it’s also useful for other things beyond the scope of this post.
When you calculate the power density and the energy density of your laser beam, the shape of your beam affects the damage thresholds:
In both cases (power and energy damage thresholds), it might be difficult for you, the end user, to estimate if you are in a safe zone, especially if you are using different laser specifications than those associated to our known damage thresholds.
In the latter case, you should absolutely contact us to share your laser specifications so we can ensure you are going to use the product properly and safely. Our recommendation will generally be to expand the beam to a minimum value in order to keep the other parameters as they are.
The dimensions and weight of the detector are definitely something to consider if the detector is going to be in a tight spot during the measurement.
You can also find technical drawings at the end of each catalogue section or download detailed outline drawings on our website.
The section at the bottom of the table is useful when you are all set and want to order a product!
To receive a quote and order, please get in touch.
We sincerely hope you liked this article. This covers the most common topics related to the specifications we display in our catalogue when it comes to power detectors. Don’t forget to subscribe to our monthly newsletter if you would like to receive our next blog posts.